Device for reducing the effects of static or fading



June 12, 1934. H. H. BEVERAGE DEVICE FOR REDUCING THE EFFECTS OF' STATICOR FADING Filed Nov. 11, i952 NNW.

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W 1 Ml I.. @ws $5@ INVENToR ,maw /f 5f/H455 BY ,w'l/(A/ TroRNEY PatentedJune 12, 1934 PATENT OFFICE DEVICE FOR REDUCING THE EFFECTS OF STATIC ORFADING Harold H. Beverage, Riverhead, N. Y., assigner to RadioCorporation of America, a corporation of Delaware Application November11, 1932, Serial No. 642,172

Claims.

.1Q to repeat the signal characters at the transmitting station aplurality of times at predetermined intervals, and, at the receiver, tostore up and compare the received characters before passing the signalson to the printing mechanism. In

l? this way, any false character, such as might be due to static, whichwas not received identically in all transmissions, would be preventedfrom operating the recording mechanism, and only those signals whichwere received in every repe- ?Q tition would set up the storageapparatus to operate the printer.

Such methodof repeating signal characters has greatly increased theaccuracy of transmission, and itis one of the objects of the present ,Zinvention tofretain the advantage 'of signal repetition without actuallyrepeating the signals, and by using much simpler equipment.

Y This object is accomplished in the present invention by employing aplurality of diversity receiving systems at stations which are widelyseparated from one another in order to cont-rol, in common, a centraloflice utilization circuit. At the central oice, relays are operated bythe signals from each station. In one particular em- ,35 bodiment of thepresent invention the relay contacts are connected in parallel so thattheir combined output mitigates against fading, and in anotherembodiment the relay contacts are connected in series so that theircombined output 19 is free from local static clicks. f

Observations have shown that both fading and some kinds of static,particularly on short waves, are random and local in their occurrence,and, hence, if signals are received at two separated points neither thefading nor certain types of static will be simultaneous at bothlocations.

`An essential feature of the present invention resides in the diversityreceiving! arrangement located at each station for insuring reception,

, 6() whereina plurality of energy collectors are separated anappreciable fraction of the length of the communication wave, say of theorder of a few wave lengths. The signal, it has been found, does notfade similarly at each of the spaced energy i. ,5,5 collectors, and thepossibility, therefore, of the signal fading out equally at all of theenergy collectors or antennae is consequently reduced with increase inthe number of antenn.

In the accompanying drawing, Figures 1 and 2 show, diagrammatically, twodiierent embodiments of radio receiving systems illustrating theprinciples of the present invention.

Figure 1 shows a system comprising two Widely separated diversityreceiving stations A and B whose individual output currents are combinedat a common central station to overcome local static clicks. At eachstation A and B is shown a diversity'receiver consisting of tworeceivers 3 and 4 which are associated with directive antenn l and 2.The output of each receiver 3 70 and 4 is rectified and the rectifiedcurrents are added together to operate a tone keying unit 5, the latterfunctioning to translate the rectified currents into currents chopped upat intervals corresponding to the interruptions of the received signalcharacters. One suitable arrangement for eiTecting such reception andtranslation, to which reference is made, is described in United StatesPatent 1,874,866, granted August 30, 1932 to Messrs. H. H. Beverage andH. O. Peterson.

The receivers at stations A and B are tuned to the same signals, and theoutputs of the tone keyers 5 are sent to a central oilice over wirelines 31 and 33. The signals are there further amplified by amplifiers35 and 37, and are then 35 rectified by rectiers 7 and 9 which, in turn,cause the operation of relays 11 and 27, respectively.

Relay tongues 13 and 19 of Figure 1 are connected in series so that bothrelays must close before utilization circuit 29 operates, a conditionwhich must exist for anti-static. As an illustration, if a static crashis received at station A, but not at station B, relay 1l will close, but

cause relay 27 is open. The utilization circuit .29 may, of course, be aprinter, recorder, or any other suitable device.

It has been suspected from observations, that some short wave staticcame from long distances by sky Wave, similar to the manner in whichshort wave signals are propagated. This was believed to be true, becausethe directional static distribution on short waves was found to besimilar to the long distance static on long waves, although theintensity of the short wave static was much less than on long Waves. Onthe other hand, it has also been noticed that local thunder storms donot create severe disturbances except when the storm is within a fewmiles of the receiving station. Even then, the disturbances are usuallysharp clicks associated directly with lightning flashes.

If it is assumed that short wave static is propagated like short wavesignals, the observations mentioned above are quite logical. Localstatic produced by local lightning storms would produce electricaldisturbances that travel along the ground as ground waves. The energywould be rapidly attenuated by losses in the grcund, and the ground wavewould quickly disappear. Hence the static might exhibit skip effects thesame as signals. The ground wave from a storm 50 miles away might beinaudible, although disturbances from the same storm might be audiblethousands of miles away via the sky wave route.

Therefore, if we assume that station A is at Riverhead, Long Island, forexample, and station B is at a point in New Jersey, more than 100 milesaway, a local storm in New Jersey wouldv be inaudible at Riverhead, andvice Versa. Under these conditions, a click from a lightning iiash atstation B would not occur at station A and its eiect would be eliminatedat the central ofce, because only one of the relays 11 and 27 wouldclose.

If local storms were in progress at both stations, the clicks would beentirely random, and both relays would close simultaneously only at rareintervals.

As an alternative, the distance transmitter might radiate energy forspace and interrupt it for mark. Both relays would normally be closedfor space and open for mark and the recorder would be adjustedaccordingly. Now if static prevented the relay from opening at onestation, but not at the other, the recorder would still be operatedcorrectly by the relay that opened.

Much of the long distance static, it has been found, may be eliminatedby directive reception and this is effected in the present invention bythe proper positioning of antennae 1 and 2, thus enabling accuratereception free from effects of distant static or fading. A similararrangement to that shown in Figure 1 may be used for anti-fading byconnecting the tongues of relays 11 and 27 in parallel in the mannerillustrated in Figure 2. If the signal fades out for a few seconds oreven minutes at one station, but not at the second station, the recorderwill operate correctly, as it will register when either relay closes.The parallel relay anti-fading arrangement should be useful inovercoming the condition which is termed Territorial Fading. This is thecondition where the signal fades simultaneously over a large area, butmay still be received well, say, fifty miles away. This condition hasbeen observed on numerous occasions.

An advantage of the present invention is that the separation of the tworeceiving stations in entirely different locations guards againstinterruptions due to power or tone line failures, fires, sleet, or anyother disaster that might interrupt the service at a single station foran extended period of time.

I claim:

1. A radio receiving system comprising a plurality of widely separateddiversity receiving stations, each of said stations including at leasttwo spaced antennae, circuit apparatus at each station for receiving andrectifying the currents received at each antenna and for additivelycombining the rectified currents, a tone keyer at each station fortranslating the combined rectied currents into alternating currentschopped up at intervals corresponding to the interruptions of thereceived signal characters, a cential oice, and lines extending fromeach tone keyer to said central oiiice, relay apparatus at said centraloiilce under control of the signals sent out by said tone keyers, and autilization circuit responsive to the operation of said relay apparatus.

2. A system as defined in claim 1 including amplifier and rectifierapparatus at said central oice for amplifying and rectifying the signalsfrom said tone keyers, said relay apparatus being connected to saidrectiers.

3. A radio receiving system comprising a plurality of widely separateddiversity receiving stations, each of said stations including at leasttwo spaced antennae, circuit apparatus at each station for receiving andrectifying the signals received in said antenna and for additivelycombining the rectified currents, a tone keyer at each station fortranslating the combined rectified currents into alternating currentschopped up at intervals corresponding to the interruptions of thereceived signal characters, a central oflice, and lines extending fromeach tone keyer to said central ofce, amplifier, rectifier and relayapparatus at said central ofiice in circuit with each tone keyer,contacts for said relay apparatus, and a utilization circuit seriallyconnected with said contacts and operable only upon the operation of allsaid relay contacts.

4. A radio receiving system comprising a plurality of widely separateddiversity receiving stations, each of said stations including at leasttwo spaced antenna, circuit apparatus at each station for receiving andrectifying the signals received in said antennae and for additivelycombining the rectied currents, a tone keyer at each station fortranslating said combined rectified currents into alternating currentschopped up at intervals corresponding to the interruptions of thereceived signal characters, a central oice, and lines extending fromleach tone keyer to said central oiiice, amplifier, rectifier and relayapparatus at said central office in circuit with each tone keyer,contacts for said relay apparatus, and a utilization circuit, saidcontacts being connected in parallel to said utilization circuit.

5. The method of operating a receiving system comprising a plurality ofwidely separated diversity receivers, each of said receivers includingat least two spaced antennae, and a central office circuit connected incommon to said receivers which includes receiving the signal at each ofsaid widely separeted diversity receivers, rectifying the signalsreceived from the individual antenn at each receiver and additivelycombining them at said receivers, and subsequently translating therectiiied energies into alternating currents, transmitting saidalternating currents to said central oiiice and rectifying saidalternating currents to effect signal reception.

HAROLD H. BEVERAGE.

